Evolution of a radio access method and a radio network of a cellular mobile communication (hereinafter, referred to as “Long Term Evolution (LTE)” or “Evolved Universal Terrestrial Radio Access (EUTRA)”) has been investigated in the third generation partnership project (3rd Generation Partnership Project: 3GPP). In the LTE, as a communication system of a wireless communication (downlink) from a base station apparatus to a mobile station apparatus, used is an orthogonal frequency division multiplexing (Orthogonal Frequency Division Multiplexing: OFDM) system that is multi-carrier transmission. As a communication system of a wireless communication (uplink) from a mobile station apparatus to a base station apparatus, used is an SC-FDMA (Single-Carrier Frequency Division Multiple Access) system that is single-carrier transmission.
In the LTE, a base station apparatus, using downlink control information (DCI) transmitted by a PDCCH (Physical Downlink Control Channel), instructs a mobile station apparatus to perform initial transmission or retransmission of a PUSCH (Physical Uplink Shared Channel) that is a channel for uplink data (Transport block) transmission. The base station apparatus receives a PUSCH which the mobile station apparatus transmits, and transmits, by a PHICH (Physical HARQ Indicator Channel), a HARQ (Hybrid Automatic Repeat reQuest) indicator indicating a decoding result of the PUSCH.
A HARQ indicator indicates ACK or NACK. When the base station apparatus succeeds in decoding a PUSCH, the HARQ indicator indicates ACK (ACKnowledgement), and when the base station apparatus fails in decoding the PUSCH, the HARQ indicator indicates NACK (Negative ACKnowledgement).
The mobile station apparatus, first, performs detection of a signal by a PHICH. The mobile station apparatus, when detecting a signal by the PHICH, sets a HARQ feedback to ACK or NACK which a HARQ indicator received by the PHICH indicates. The mobile station apparatus, when detecting no signal by the PHICH, sets a HARQ feedback to nothing (a state of the HARQ feedback is maintained).
Then, the mobile station apparatus performs detection of downlink control information. The mobile station apparatus, when having received the downlink control information instructing initial transmission of a PUSCH, determines uplink data transmitted by a PUSCH, stores this uplink data in a HARQ buffer, performs initial transmission of a PUSCH in accordance with the downlink control information, and sets a HARQ feedback to NACK. The mobile station apparatus, when having received the downlink control information instructing retransmission of a PUSCH, performs, by a PUSCH, retransmission of uplink data stored in a HARQ buffer in accordance with the downlink control information, and sets a HARQ feedback to NACK. Note that the mobile station apparatus, when having detected the downlink control information instructing initial transmission or retransmission of a PUSCH, does not perform an operation based on a HARQ indicator (that is, ACK or NACK set to HARQ feedback) received by a PHICH.
The mobile station apparatus, when having not received the downlink control information for a PUSCH, performs transmission of a PUSCH based on a HARQ feedback which has been set. The mobile station apparatus, when NACK is set to a HARQ feedback, performs retransmission of a PUSCH, and when ACK is set to a HARQ feedback, does not perform transmission of a PUSCH, and keeps data stored in a HARQ buffer. The mobile station apparatus, when NACK is set to a HARQ feedback, until receiving, by a PHICH, a HARQ indicator which indicates ACK, or until receiving, by PDCCH, newly the downlink control information for a PUSCH, performs retransmission of a PUSCH based on the downlink control information received last. For example, the mobile station apparatus, when having detected no signal by a PHICH in a state where NACK is set to a HARQ feedback, performs retransmission of a PUSCH.
In 3GPP, a radio access system and a radio network which realize higher-speed data communication using a frequency band wider than the LTE (hereinafter, referred to as “Long Term Evolution-Advanced” (LTE-A) or “Advanced Evolved Universal Terrestrial Radio Access” (A-EUTRA)) has been investigated. In the LTE-A, it is requested to have backward compatibility with the LTE, that is, it is requested that a base station apparatus of the LTE-A performs wireless communication with mobile station apparatuses of both LTE-A and LTE simultaneously, and that a mobile station apparatus of the LTE-A is made to be able to perform wireless communication with base station apparatuses of both LTE-A and LTE, and it has been investigated that the LTE-A uses the same channel structure as the LTE.
In the LTE-A, a technology (frequency band aggregation; referred to also as Spectrum aggregation, Carrier aggregation, Frequency aggregation or the like.) has been investigated in which frequency bands of the same channel structure as the LTE (hereinafter, referred to as “component carrier (CC)”) are aggregated, and used as one frequency band (wide frequency band). Specifically, in a communication using frequency aggregation, a downlink channel is transmitted for every downlink component carrier, and an uplink channel is transmitted for every uplink component carrier. That is, the frequency aggregation is a technology by which a base station apparatus and a plurality of mobile station apparatuses transmit and receive a plurality of pieces of data and a plurality of pieces of control information simultaneously using a plurality of channels, a plurality of component carriers in an uplink and a downlink.
In a communication using the frequency aggregation, it has been proposed that a base station apparatus sets a downlink component carrier and an uplink component carrier which are used for communication to a mobile station apparatus using an RRC signal (Radio Resource Control signal) or the like, and notifies, using a PDCCH or a MAC (Medium Access Control) CE (Control Element) or the like, of an activation command which indicates a downlink component carrier used for downlink communication from among the set downlink component carriers. (Non-patent document 1)